Intravenous iron therapy and circulating biomarkers of inflammation in men with heart failure with reduced ejection fraction

Background

Large randomized clinical trials have demonstrated that intravenous (IV) iron therapy in iron-deficient patients with heart failure with reduced ejection fraction (HFrEF) brings clinical benefits related to symptoms of the disease and exercise capacity. Mechanisms underlying beneficial effects of such repletion are still the subject of interest as this is not solely related to improved haematopoiesis (IV iron works also in non-anaemic subjects). In patients with chronic heart failure iron deficiency (ID) is linked with inflammatory processess but data regarding the impact of IV iron on inflammation is scarce.

Purposes

We evaluated whether IV iron therapy affects circulating biomarkers of pro-inflammatory state in men with HFrEF and concomitant ID.

Methods

This is the sub-analysis of the study to investigate the effects of IV ferric carboxymaltose (FCM) on the functioning of skeletal muscles in men with HFrEF. For the purposes of current research we analyzed data of 20 men with HFrEF (median age 68 (62, 75 – in brackets interquartile ranges, respectively) years, LVEF: 30 (25, 35) %, ischaemic HF aetiology: 85%, NYHA class I/II/III: 30%/50%/20%) and ID (definition according to ESC guidelines - ferritin <100 ng/mL, or ferritin 100–299 ng/mL with transferrin saturation [TSAT] <20%) who were randomized in a 1:1 ratio to receive either the 24-week therapy with IV FCM (dosing scheme as in the CONFIRM-HF trial) or saline (controls). The study was double-blinded. We used ELISA to evaluate different circulating pro-inflammatory biomarkers (high-sensitivity C-reactive protein [hs-CRP], tumor necrosis factor alpha [TNF-α], interleukin 6 [IL-6], interleukin 1 beta [IL-1β], interleukin 22 [IL-22]) at baseline and week 24.

Results

IV FCM therapy repleted iron stores in men with HFrEF as reflected by an increase in serum ferritin and TSAT, which was not seen in a control group. IV FCM therapy (as well as the saline administration) affected neither haemoglobin concentration nor parameters reflecting iron stores in red cells.

Baseline serum ferritin was not related to hs-CRP, TNF-α, IL-6, IL-1β, and IL-22 (all p>0.23). Baseline TSAT was related to hs-CRP (r=−0.47, p=0.02) but not other inflammatory biomarkers.

Levels of hs-CRP, TNF-α, IL-6, IL-1β, and IL-22 at week 0 were similar in subjects who received IV iron and controls (all p>0.22).

Change from week 0 to week 24 adjusted for baseline value (delta W24-W0 as the percentage of W0) regarding IL-22 was lower in an active treatment arm as compared with saline (p=0.049) and there was a trend towards lower delta TNF-α in FCM group compared to saline (p=0.067). These findings were not valid for other measured pro-inflammatory biomarkers.

Conclusions

In men with HFrEF and concomitant ID intravenous iron therapy with FCM affects biomarkers of pro-inflammatory state. Clinical relevance of this finding requires further translational research.

Funding Acknowledgement

Type of funding source: Public grant(s) – National budget only. Main funding source(s): This research was funded by the National Science Centre (Poland) grant allocated on the basis of the decision number DEC-2012/05/E/NZ5/00590

Iron deficiency as energetic insult to skeletal muscle in chronic diseases

Specific skeletal myopathy constitutes a common feature of heart failure, chronic obstructive pulmonary disease, and type 2 diabetes mellitus, where it can be characterized by the loss of skeletal muscle oxidative capacity. There is evidence from in vitro and animal studies that iron deficiency affects skeletal muscle functioning mainly in the context of its energetics by limiting oxidative metabolism in favour of glycolysis and by alterations in both carbohydrate and fat catabolic processing. In this review, we depict the possible molecular pathomechanisms of skeletal muscle energetic impairment and postulate iron deficiency as an important factor causally linked to loss of muscle oxidative capacity that contributes to skeletal myopathy seen in patients with heart failure, chronic obstructive pulmonary disease, and type 2 diabetes mellitus.

Depleted iron stores are associated with inspiratory muscle weakness independently of skeletal muscle mass in men with systolic chronic heart failure

BACKGROUND

Skeletal and respiratory muscle dysfunction constitutes an important pathophysiological feature of heart failure (HF). We assessed the relationships between respiratory muscle function, skeletal muscle mass, and physical fitness in men with HF with reduced left ventricular ejection fraction (HFrEF), and investigated the hypothesis of whether iron deficiency (ID) contributes to respiratory muscle dysfunction in these patients.

METHODS

We examined 53 male outpatients with stable HFrEF without asthma or chronic obstructive pulmonary disease (age: 64 ± 10 years; New York Heart Association [NYHA] class I/II/III: 36/51/13%; ischaemic aetiology: 83%; all with left ventricular ejection fraction ≤40%) and 10 middle-aged healthy men (control group). We analysed respiratory muscle function (maximal inspiratory and expiratory pressure at the mouth [MIP and MEP, respectively]), appendicular lean mass/body mass index (ALM/BMI; ALM was measured using dual-energy X-ray absorptiometry), physical fitness (components of Functional Fitness Test for Older Adults), and iron status.

RESULTS

MIP, MEP, and ALM/BMI (but not MIP adjusted for ALM/BMI) were lower in men with HFrEF vs. healthy men. MIP, MEP, and MIP adjusted for ALM/BMI (but not ALM/BMI) were lower in men with HFrEF with vs. without ID. In a multivariable linear regression model lower serum ferritin (but not transferrin saturation) was associated with lower MIP independently of ALM/BMI, left ventricular ejection fraction, N-terminal pro-B-type natriuretic peptide (NT-proBNP), and haemoglobin concentration. In multivariable linear regression models, lower MIP was associated with worse results in Functional Fitness Test when adjusted for ALM/BMI or relevant clinical variables (NYHA class, estimated glomerular filtration rate, NT-proBNP, and haemoglobin concentration).

CONCLUSIONS

In men with HFrEF, low ferritin reflecting depleted iron stores is associated with inspiratory muscle weakness independently of skeletal muscle mass. Inspiratory muscle dysfunction correlates with worse physical fitness independently of either skeletal muscle mass or disease severity.

Iron limitation promotes the atrophy of skeletal myocytes, whereas iron supplementation prevents this process in the hypoxic conditions

There is clinical evidence that patients with heart failure and concomitant iron deficiency have increased skeletal muscle fatigability and impaired exercise tolerance. It was expected that a skeletal muscle cell line subjected to different degrees of iron availability and/or concomitant hypoxia would demonstrate changes in cell morphology and in the expression of atrophy markers. L6G8C5 rat skeletal myocytes were cultured in normoxia or hypoxia at optimal, reduced or increased iron concentrations. Experiments were performed to evaluate the iron content in cells, cell morphology, and the expression of muscle specific atrophy markers [Atrogin1 and muscle-specific RING-finger 1 (MuRF1)], a gene associated with the atrophy/hypertrophy balance [mothers against decapentaplegic homolog 4 (SMAD4)] and a muscle class-III intermediate filament protein (Desmin) at the mRNA and protein level. Hypoxic treatment caused, as compared to normoxic conditions, an increase in the expression of Atrogin-1 (P<0.001). Iron-deficient cells exhibited morphological abnormalities and demonstrated a significant increase in the expression of Atrogin-1 (P<0.05) and MuRF1 (P<0.05) both in normoxia and hypoxia, which indicated activation of the ubiquitin proteasome pathway associated with protein degradation during muscle atrophy. Depleted iron in cell culture combined with hypoxia also induced a decrease in SMAD4 expression (P<0.001) suggesting modifications leading to atrophy. In contrast, cells cultured in a medium enriched with iron during hypoxia exhibited inverse changes in the expression of atrophy markers (both P<0.05). Desmin was upregulated in cells subjected to both iron depletion and iron excess in normoxia and hypoxia (all P<0.05), but the greatest augmentation of mRNA expression occurred when iron depletion was combined with hypoxia. Notably, in hypoxia, an increased expression of Atrogin-1 and MuRF1 was associated with an increased expression of transferrin receptor 1, reflecting intracellular iron demand (R=0.76, P<0.01; R=0.86, P<0.01). Hypoxia and iron deficiency when combined exhibited the most detrimental impact on skeletal myocytes, especially in the context of muscle atrophy markers. Conversely, iron supplementation in in vitro conditions acted in a protective manner on these cells.

Both iron excess and iron depletion impair viability of rat H9C2 cardiomyocytes and L6G8C5 myocytes

BACKGROUND

Iron is presumed to play an important role in the functioning of cardiomyocytes and skeletal myocytes. There is scarcity of direct data characterising the cells functioning when exposed to iron depletion or iron overload in a cellular environment. There is some clinical evidence demonstrating that iron deficiency has serious negative prognostic consequences in heart failure (HF) patients and its correction brought clinical benefit.

AIM

The viability of the cells upon unfavourable iron concentration in the cell culture medium and the presence of the molecular system of proteins involved in intracellular iron metabolism in these cells have been studied.

METHODS

H9C2 rat adult cardiomyocytes and L6G8C5 rat adult skeletal myocytes were cultured for 24 h in optimal vs. reduced vs. increased iron concentrations. Intracellular iron content was measured by flame atomic absorption spectroscopy (FAAS). We analysed the mRNA expression of: ferritin heavy and light chains (FTH and FTL; iron storage proteins), myoglobin (MB, oxygen storage protein) ferroportin type 1 (FPN1; iron exporter), transferrin receptor type 1 (TfR1; iron importer), hepcidin (HAMP; iron metabolism regulator) using qPCR, the level of respective proteins using Western Blot (WB), and the viability of the cells using flow cytometry and cell viability tetrazolium reduction assay (MTS).

RESULTS

Cardiomyocytes exposed to gradually reduced iron concentrations in the medium demonstrated a decrease in the mRNA expression of FTH, FTL, FPN1, MB, and HAMP (all R = -0.75, p < 0.05), indicating depleted iron status in the cells. As a consequence, the expression of TfR1 (R = 0.7, p < 0.05) was increased, reflecting a facilitated entrance of iron to the cells. The inverse changes occurred in H9C2 cells exposed to increased iron concentrations in the medium in comparison to control cells. The same pattern of changes in the mRNA expressions was observed in myocytes, and there was a strong correlation between analogous genes in both cell lines (all R > 0.9, p < 0.0001). WB analysis revealed the analogous pattern of changes in protein expression as an mRNA profile. Both iron depletion and iron excess impaired viability of cardiomyocytes and skeletal myocytes.

CONCLUSIONS

Both rat cardiomyocytes and myocyte cells contain the set of genes involved in the intracellular iron metabolism, and both types of investigated cells respond to changing iron concentrations in the cultured environment. Both iron deficiency (ID) and iron overload is detrimental for the cells. This data may explain the beneficial effects of iron supplementation in patients with ID in HF.

Influence of the availability of iron during hypoxia on the genes associated with apoptotic activity and local iron metabolism in rat H9C2 cardiomyocytes and L6G8C5 skeletal myocytes

The differential availability of iron during hypoxia is presumed to affect the functioning of cardiac and skeletal myocytes. Rat H9C2 cardiomyocytes and L6G8C5 myocytes were cultured for 48 h in normoxic or hypoxic conditions at the optimal, reduced or increased iron concentration. The mRNA expression levels of markers of apoptosis [B‑cell lymphoma‑2 (Bcl2; inhibition) and Bcl‑2‑activated X protein (Bax; induction)], atrophy (Atrogin), glycolysis (pyruvate kinase 2; PKM2) and iron metabolism [transferrin receptor 1 (TfR1; iron importer), ferroportin 1 (FPN1; iron exporter), ferritin heavy chain (FTH; iron storage protein) and hepcidin (HAMP; iron regulator)] were determined using reverse transcription‑quantitative polymerase chain reaction, and cell viability was measured using an tetrazolium reduction assay. Cardiomyocytes and myocytes, when exposed to hypoxia, demonstrated an increased Bax/Bcl‑2 gene expression ratio (P<0.05). Additional deferoxamine (DFO) treatment resulted in further increases in Bax/Bcl‑2 in each cell type (P<0.001 each) and this was associated with the 15% loss in viability. The analogous alterations were observed in both cell types upon ammonium ferric citrate (AFC) treatment during hypoxia; however, the increased Bax/Bcl‑2 ratio and associated viability loss was lower compared with that in case of DFO treatment (P<0.05 each). Under hypoxic conditions, myocytes demonstrated an increased expression of PKM2 (P<0.01). Additional DFO treatment caused an increase in the mRNA expression levels of PKM2 and Atrogin‑1 (P<0.001 and P<0.05, respectively), whereas AFC treatment caused an increased mRNA expression of PKM2 (P<0.01) and accompanied decreased mRNA expression of Atrogin‑1 (P<0.05). The expression augmentation of PKM2 during hypoxia was greater upon low iron compared with that of ferric salt treatment (P<0.01). Both cell types upon DFO during hypoxia demonstrated the increased expression of TfR1 and HAMP (all P<0.05), which was associated with the increased Bax/Bcl‑2 ratio (all R>0.6 and P<0.05). In conclusion, during hypoxia iron deficiency impairs the viability of cardiomyocytes and myocytes more severely compared with iron excess. In myocytes, during hypoxia iron may act in a protective manner, since the level of atrophy is decreased in the iron‑salt‑treated cells.

Search for the Function of NWC, Third Gene Within RAG Locus: Generation and Characterization of NWC-Deficient Mice

NWC is a third gene within recombination activating gene (RAG) locus, which unlike RAG genes is ubiquitously expressed and encodes a unique protein containing three strongly evolutionarily conserved domains not found in any other known protein. To get insight into its function we identified several proteins co-immunoprecipitating with NWC protein and generated new NWC-deficient mice. Here, we present evidence that unlike many other ubiquitously expressed evolutionarily conserved proteins, functional inactivation of NWC does not cause any gross developmental, physiological or reproductive abnormalities and that under physiological conditions NWC may be involved in assembling and functioning of cilia, cell surface organelles found on nearly every eukaryotic cell.